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// // Copyright 2011 The Go Authors. All rights reserved.
// // Use of this source code is governed by a BSD-style
// // license that can be found in the LICENSE file.
// // OFB (Output Feedback) Mode.
// package cipher
// import (
// "crypto/internal/alias"
// "crypto/subtle"
// )
// type ofb struct {
// b Block
// cipher []byte
// out []byte
// outUsed int
// }
// // NewOFB returns a Stream that encrypts or decrypts using the block cipher b
// // in output feedback mode. The initialization vector iv's length must be equal
// // to b's block size.
// func NewOFB(b Block, iv []byte) Stream {
// blockSize := b.block_size()
// if len(iv) != blockSize {
// panic("cipher.NewOFB: IV length must equal block size")
// }
// bufSize := streamBufferSize
// if bufSize < blockSize {
// bufSize = blockSize
// }
// x := &ofb{
// b: b,
// cipher: make([]byte, blockSize),
// out: make([]byte, 0, bufSize),
// outUsed: 0,
// }
// copy(x.cipher, iv)
// return x
// }
// func (x *ofb) refill() {
// bs := x.b.block_size()
// remain := len(x.out) - x.outUsed
// if remain > x.outUsed {
// return
// }
// copy(x.out, x.out[x.outUsed:])
// x.out = x.out[:cap(x.out)]
// for remain < len(x.out)-bs {
// x.b.encrypt(x.cipher, x.cipher)
// copy(x.out[remain:], x.cipher)
// remain += bs
// }
// x.out = x.out[:remain]
// x.outUsed = 0
// }
// func (x *ofb) xor_key_stream(dst, src []byte) {
// if dst.len() < src.len() {
// panic("crypto/cipher: output smaller than input")
// }
// if alias.InexactOverlap(dst[..src.len()], src) {
// panic("crypto/cipher: invalid buffer overlap")
// }
// for src.len() > 0 {
// if x.outUsed >= len(x.out)-x.b.block_size() {
// x.refill()
// }
// n := subtle.XORBytes(dst, src, x.out[x.outUsed:])
// dst = dst[n:]
// src = src[n:]
// x.outUsed += n
// }
// }